From this story on cbsnews.com:Ten young whooping cranes and the bird-like plane they think is their mother had flown more than halfway to their winter home in Florida when federal regulators stepped in. Now the birds and the plane are grounded in Alabama while the Federal Aviation Administration investigates whether the journey violates regulations because the pilot was being paid by a conservation group to lead the cranes on their first migration instead of working for free.

FAA regulations say only pilots with commercial pilot licenses can fly for hire. The pilots of Operation Migration's plane are instead licensed to fly sport aircraft because that's the category of aircraft that the group's small, open plane with its rear propeller and bird-like wings falls under. FAA regulations also prohibit sport aircraft "which are sometimes of exotic design" from being flown to benefit a business or charity. The rules are aimed, in part, at preventing businesses or charities from taking passengers for joyrides in sometimes risky planes. "That's a valid rule. They shouldn't be hired to do that. But it wasn't written, I believe, to stop a wildlife reintroduction," Joe Duff, an Operation Migration co-founder and one of its pilots, said. The conservation group has agreed voluntarily to stop flying and has applied to FAA for a waiver. "We're considering that waiver," FAA spokesman Lynn Lunsford said. He said he didn't know when a decision would be made or whether it would be made before spring, when the birds would return to Wisconsin.